Precursor for preparing lithium composite transition metal oxide and method for preparing the same

ABSTRACT

Disclosed is a transition metal precursor used for preparation of lithium composite transition metal oxide, the transition metal precursor comprising a composite transition metal compound represented by the following Formula 1: 
       M(OH 1−x ) 2−y A y/n   (1)
         wherein   M comprises two or more selected from the group consisting of Ni, Co, Mn, Al, Cu, Fe, Mg, B, Cr and second period transition metals;   A comprises one or more anions except OH 1−x ;   0&lt;x&lt;0.5;   0.01≦y≦0.5; and   n is an oxidation number of A.       

     The transition metal precursor according to the present invention contains a specific anion. A lithium composite transition metal oxide prepared using the transition metal precursor comprises the anion homogeneously present on the surface and inside thereof, and a secondary battery based on the lithium composite transition metal oxide thus exerts superior power and lifespan characteristics, and high charge and discharge efficiency.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 14/452,833filed on Aug. 6, 2014, which is a continuation of InternationalApplication No. PCT/KR2013/001722 filed on Mar. 5, 2013, which claimsthe benefit of Korean Patent Application No. 10-2012-0027119, filed onMar. 16, 2012, the disclosures of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a precursor used for preparation oflithium composite transition metal oxide and a method for preparing thesame. More specifically, the present invention relates to a transitionmetal precursor used for preparation of lithium composite transitionmetal oxide comprising a specific composite transition metal compoundand a method for preparing the same.

BACKGROUND ART

Technological development and increased demand for mobile equipment haveled to a rapid increase in demand for secondary batteries as energysources. Among these secondary batteries, lithium secondary batterieshaving high energy density and voltage, long cycle span and lowself-discharge are commercially available and widely used.

Lithium-containing cobalt oxide (LiCoO₂) is generally used as a cathodeactive material for lithium secondary batteries. Use oflithium-containing manganese oxides such as LiMnO₂ having alayered-crystal structure and LiMn₂O₄ having a spinel-crystal structure,and lithium-containing nickel oxide (LiNiO₂) is also considered.

Among these cathode active materials, LiCoO₂ is the most generally usedowing to superior physical properties such as superior cyclecharacteristics, but has low stability and is costly due to resourcelimitations of cobalt as a raw material.

Lithium manganese oxides such as LiMnO₂ and LiMn₂O₄ advantageously use,as a raw material, manganese which is abundant and eco-friendly, thusattracting much attention as a cathode active material alternative toLiCoO₂. However, these lithium manganese oxides have disadvantages oflow capacity and bad cycle characteristics.

In addition, lithium nickel oxides such as LiNiO₂ are cheaper thancobalt oxides and have higher discharge capacity, when charged to 4.25V.More specifically, doped LiNiO₂ has a reversible capacity of about 200mAh/g which is higher than LiCoO₂ capacity (about 153 mAh/g).Accordingly, in spite of slightly low average discharge voltage andvolumetric density, commercial batteries comprising LiNiO₂ as a cathodeactive material have improved energy density and a great deal ofresearch into these nickel-based cathode active materials is thusactively conducted in order to develop high-capacity batteries recently.

In this regard, many conventional techniques focus on properties ofLiNiO₂-based cathode active materials and improvement in preparationprocess of LiNiO₂ and suggest lithium transition metal oxides whereinnickel is partially substituted by other transition metal such as Co orMn. However, the problems of LiNiO₂-based cathode active materialsincluding high preparation costs, swelling caused by gas generation inbatteries, low chemical stability and high pH have been satisfactorilynot yet solved.

Accordingly, in the related art, there is an attempt to improveperformance of batteries by applying a material such as LiF, Li₂SO₄ orLi₃PO₄ to the surface of lithium nickel-manganese-cobalt oxide. In thiscase, the substance is disposed only on the surface of the lithiumnickel-manganese-cobalt oxide, thus disadvantageously having alimitation on exertion of effects to a desired level and requiring aseparate process for application of the material to the surface thereof.

However, in spite of such various attempts, lithium composite transitionmetal oxide exhibiting satisfactory performance has yet to be developed.

DISCLOSURE Technical Problem

Therefore, the present invention has been made to solve the above andother technical problems that have yet to be resolved.

As a result of a variety of extensive and intensive studies andexperiments to solve the problems as described above, the presentinventors developed a precursor containing a composite transition metalcompound having a specific anion and discovered that secondary batteriesbased on lithium composite transition metal oxide produced from theprecursor exhibit superior power and lifespan characteristics and havesuperior charge/discharge efficiency. The present invention has beencompleted based on this discovery.

Technical Solution

Accordingly, the present invention provides a transition metal precursorused for preparation of lithium composite transition metal oxide whichis an electrode active material for lithium secondary batteries, thetransition metal precursor comprising a composite transition metalcompound represented by the following Formula 1:

M(OH_(1−x))_(2−y)A_(y/n)  (1)

-   -   wherein    -   M comprises two or more selected from the group consisting of        Ni, Co, Mn, Al, Cu, Fe, Mg, B, Cr and second period transition        metals;    -   A comprises one or more anions except OH_(1−x);    -   0<x<0.5;    -   0.01≦y≦0.5; and    -   n is an oxidation number of A.

Methods including doping or surface-treating an electrode activematerial for conventional lithium secondary batteries with a lithiumcompound comprising a specific anion such as F⁻, PO₄ ³⁻ or CO₃ ²⁻, ormixing the same with the lithium compound are known. For example, oneconventional method suggests an electrode active material for secondarybatteries obtained by mixing conventional lithium nickel-based oxidewith lithium phosphate having a specific structure. Another conventionalmethod is use of lithium manganese-based oxide coated with lithiumphosphate as an electrode active material in order to prevent elution ofmanganese ions from an electrolyte solution.

However, these conventional methods require an additional process suchas surface-treatment of the electrode active material with a lithiumcompound after preparation of the electrode active material, thuscausing an increase in manufacturing costs of lithium secondarybatteries. In addition, it is difficult to accomplish a desired level ofeffects, since specific anions are present on only the surface of theelectrode active material.

Accordingly, the transition metal precursor according to the presentinvention is substituted by a specific amount of one or more anionsexcept for OH_(1−X). The inventors of the present application discoveredthat the anions may be homogeneously present on the surface and theinside of lithium composite transition metal oxide when lithiumcomposite transition metal oxide is prepared using the anion-substitutedprecursor and newly established that secondary batteries based on theprecursor possess superior power and lifespan and exhibit high chargeand discharge efficiency.

That is, the specific anions homogeneously present on the surface andthe inside of the lithium composite transition metal oxide contribute toimprovement in ion conductivity between grains and reduce sizes of growngrains or crystals, thus reducing structure variation upon generation ofoxygen in the activation process, increasing surface area and therebyimproving performance required for batteries such as ratecharacteristics.

In Formula 1, M comprises two or more selected from the elements definedabove.

In a preferred embodiment, M comprises one or more transition metalsselected from the group consisting of Ni, Co and Mn and imparts physicalproperties of at least one of the transition metals to lithium compositetransition metal oxide. Particularly preferably, M comprises two typesof transition metals selected from the group consisting of Ni, Co andMn, or all the transition metals.

In addition, in Formula 1, there is no limitation as to the anion A solong as the anion A contributes to improvement in ion conductivitybetween grains.

In a preferred embodiment, A comprises one or more selected from thegroup consisting of PO₄, CO₃, BO₃, and F. Of these, PO₄ is particularlypreferred since it has a considerably stable structure and a highlithium diffusion coefficient when bonded to lithium, thus improvingstability of the lithium composite transition metal oxide.

When a content of the anion A is excessively high, the anion Ainterferes with crystallization of lithium composite transition metaloxide comprising the same and makes improvement in active materialperformance difficult. When the content is excessively low, it isdifficult to achieve desired effects. The content of A in the compositetransition metal compound is preferably 0.01 to 0.5 mol %, particularlypreferably not less than 0.03 and not more than 0.2 mol %, based on thetotal amount (in mol) of the composite transition metal compound, asdescribed above.

For reference, the content of the anion A is determined within the rangeaccording to the oxidation number of the anion, as described above.

A preferred example of the composite transition metal compound includesa composite transition metal compound represented by the followingFormula 2.

Ni_(b)Mn_(c)Co_(1−(b+c+d))M′_(d)(OH_(1−x))_(2−y)A_(y/n)  (2)

-   -   wherein 0.3≦b≦0.9, 0.1≦c≦0.6, 0≦d≦0.1, b+c+d≦1; M′ comprises one        or two or more selected from the group consisting of Al, Mg, Cr,        Ti, Si, Cu, Fe and Zr; and A, x, y and n are as defined in        Formula 1 above.

The composite transition metal compound comprises a high content ofnickel and is particularly preferable for preparation of cathode activematerials for high-capacity lithium secondary batteries. That is,regarding the content (b) of nickel, nickel is present in an excessamount, as compared to manganese and cobalt, based on the total amount(in unit of mol) and is 0.3 to 0.9, as defined above. When the contentof the nickel is lower than 0.3, it is difficult to obtain highcapacity, and when the content of the nickel exceeds 0.9,disadvantageously, safety is greatly deteriorated. More preferably, thecontent of nickel is 0.33 to 0.8.

In addition, the content (c) of manganese is 0.1 to 0.6, preferably 0.1to 0.5, as defined above.

In some cases, the metal, M′ may be substituted within the range of 0.1or less by one, or two or more selected from the group consisting of Al,Mg, Cr, Ti and Si and is preferably substituted within the range of 0.08or less.

The content (1−(b+c+d)) of cobalt is changed according to a sum (b+c+d)of the contents of nickel, manganese and the metal M′. When the contentof cobalt is excessively high, overall cost of raw materials increasesdue to high content of cobalt and reversible capacity slightlydecreases, and when the content thereof is excessively low, it may bedifficult to obtain both sufficient rate characteristics and high powderdensity of batteries. Accordingly, the sum (b+c+d) of the contents ofnickel, manganese and metal M′ is preferably 0.05 to 0.4.

Such a transition metal compound having a high tap density since itcomprises the anion A. In a preferred embodiment, the transition metalcompound has a tap density of 1.5 to 2.5 g/cc.

The transition metal precursor according to the present invention atleast comprises the composite transition metal compound of Formula 1. Ina preferred embodiment, the transition metal precursor comprises thecomposite transition metal compound in an amount of 30% by weight ormore, more preferably 50% by weight or more.

As compared to a transition metal precursor comprising no compositetransition metal compound of Formula 1, the transition metal precursorcan be prepared using lithium composite transition metal oxideexhibiting superior physical properties, as can be seen from Examplesand Experimental Examples described later.

The remaining component of the transition metal precursor may bevariable and is for example M(OH_(1−x))₂ (wherein M and x are as definedin Formula 1 above).

The present invention also provides the composite transition metalcompound of Formula 1 and the composite transition metal compound ofFormula 1 is a novel substance not previously known in the art.

The transition metal precursor comprising the composite transition metalcompound is preferably prepared by introducing a compound containing theanion A during a preparation process. As described above, the methodaccording to the present invention does not require an additionalprocess for reacting the prepared lithium composite transition metaloxide with the compound containing the anion A, thus beingdisadvantageously simple, easy and highly economically efficient. Inaddition, lithium composite transition metal oxide prepared from theprecursor exerts superior cathode active material performance, ascompared to lithium composite transition metal oxide not using theprecursor.

Hereinafter, a method for preparing the transition metal precursoraccording to the present invention will be described in detail.

The transition metal precursor may be prepared by a coprecipitationmethod using a basic substance in which a transition metal-containingsalt and an anion A-containing compound are dissolved in specificamounts.

Coprecipitation is a method for preparing the transition metal precursorby simultaneously precipitating two or more types of transition metalelements in an aqueous solution. In a specific example, the compositetransition metal compound comprising two or more types of transitionmetals may be prepared by mixing transition metal-containing salts in adesired molar ratio while considering the contents of transition metalsto prepare an aqueous solution, mixing the aqueous solution with astrong base such as sodium hydroxide and optionally maintaining a pH ata basic range through addition of an additive such as ammonia source. Inthis case, average particle diameter, particle diameter distribution andparticle density can be adjusted to desired levels by suitablycontrolling temperature, pH, reaction time, slurry concentration, ionconcentration and the like. The pH range is 9 to 13, preferably 10 to12. The reaction may be performed in multiple steps, as necessary.

The transition metal-containing salt preferably has an anion which isreadily degraded and is highly volatile, and is sulfate or nitrate,particularly preferably sulfate. Examples of the transitionmetal-containing salt include, but are not limited to, nickel sulfate,cobalt sulfate, manganese sulfate, nickel nitrate, cobalt nitrate andmanganese nitrate.

Examples of the basic substance include sodium hydroxide, potassiumhydroxide, lithium hydroxide and the like. The basic substance ispreferably sodium hydroxide, but the present invention is not limitedthereto.

In addition, the anion A-containing compound may be represented byZ_(x)′A_(y)′, wherein Z is at least one selected from the groupconsisting of Na, NH₄ and H, A is at least one selected from the groupconsisting of PO₄, CO₃, BO₃, and F, and an equation of (an oxidationnumber of Z×x′)+(an oxidation number of A×y′)=0 is satisfied, with theproviso that 0<x′<4 and 0<y′<4. In a preferred embodiment, Z_(x)′A_(y)′is one or more selected from the group consisting of Na₃PO₄, (NH₄)₃PO₄,(NH₄)₂HPO₄, and (NH₄)H₂PO₄.

The compound of Z_(x)′A_(y)′ is soluble in water and the compound ispreferably is added within the range of 0.01 to 0.5 mol % to a reactionchamber after being dissolved in the basic substance defined above,preferably in a sodium hydroxide solution, and then reacts with thetransition metal salt for preparing the precursor. In some cases, thecompound may be added together with a transition metal-containing salt.

In a preferred embodiment, in the co-precipitation process, an additiveand/or alkali carbonate which forms a complex with a transition metalmay be further added. For example, the additive may be an ammonium ionsource, an ethylene diamine compound, a citric acid compound or thelike. Examples of the ammonium ion source include ammonia water, anaqueous ammonium sulfate solution, an aqueous ammonium nitrate solutionand the like. The alkali carbonate may be selected from the groupconsisting of ammonium carbonate, sodium carbonate, potassium carbonateand lithium carbonate. A mixture of two or more of these compounds maybe used, if necessary.

The contents of the additive and alkali carbonate may be suitablydetermined while considering an amount of the transitionmetal-containing salt, pH or the like.

The transition metal precursor comprising only the composite transitionmetal compound of Formula 1 may be prepared or a transition metalprecursor comprising other composite transition metal compound inaddition to the composite transition metal compound of Formula 1 may beprepared according to reaction conditions and details thereof will beclearly understood from the examples described later.

The present invention also provides lithium composite transition metaloxide prepared from the transition metal precursor. More specifically,lithium composite transition metal oxide which is a cathode activematerial for lithium secondary batteries may be prepared by reacting thetransition metal precursor with a lithium-containing material bycalcination.

The lithium composite transition metal oxide homogenously comprises theanion A on the surface and the inside of lithium composite transitionmetal oxide, thus exhibiting superior electrochemical properties. Thecontent of the anion A may be changed according to the number of molesof A substituted in the composite transition metal compound, but ispreferably 0.05 to 3% by weight, based on the total weight of lithiumcomposite transition metal oxide.

The lithium composite transition metal oxide is preferably used as anelectrode active material for lithium secondary batteries and is usedalone or in combination thereof, or as a mixture with other well-knownelectrode active material for lithium secondary batteries.

In addition, the lithium composite transition metal oxide comprises twoor more transition metals and examples thereof include, but are notlimited to, layered compounds substituted by one or more transitionmetals such as lithium cobalt oxide (LiCoO₂) or lithium nickel oxide(LiNiO₂); lithium manganese oxide substituted by one or more transitionmetals; lithium nickel-based oxide represented by the formula ofLiNi_(1−y)M_(y)O₂ (wherein M comprises Co, Mn, Al, Cu, Fe, Mg, B, Cr,Zn, Ga, or a combination of two or more thereof, and 0.01≦y≦0.7); andlithium nickel cobalt manganese composite oxide represented byLi_(1+z)Ni_(b)Mn_(c)Co_(1−(b+c+d))MdO_((2−e))N_(e) (wherein −0.5≦z≦0.5,0.3≦b≦0.9, 0.1≦c≦0.9), 0≦d≦0.1, 0≦e≦0.05, b+c+d<1, M is Al, Mg, Cr, Ti,Si or Y, and N═F, P or Cl), such as Li_(1+z)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂,and Li_(1+z)Ni_(0.4)Mn_(0.4)Co_(0.2)O₂.

The lithium composite transition metal oxide is particularly preferablylithium composite transition metal oxide comprising Co, Ni and Mn.

Conditions for reaction between the transition metal precursor and thelithium-containing material for preparing lithium composite transitionmetal oxide are well-known in the art and a detailed explanation thereofis thus omitted.

The present invention also provides a cathode comprising the lithiumcomposite transition metal oxide as a cathode active material and alithium secondary battery comprising the cathode.

For example, the cathode is prepared by applying a mixture containing acathode active material, a conductive material and a binder to a cathodecurrent collector, followed by drying, and a filler may be furtheroptionally added to the mixture.

The cathode current collector is generally manufactured to have athickness of 3 to 500 μm. Any cathode current collector may be usedwithout particular limitation so long as it has suitable conductivitywithout causing adverse chemical changes in the fabricated battery.Examples of the cathode current collector include stainless steel,aluminum, nickel, titanium, sintered carbon, and aluminum or stainlesssteel surface-treated with carbon, nickel, titanium or silver. Thecathode current collectors include fine irregularities on the surfacethereof so as to enhance adhesion to the cathode active material. Inaddition, the cathode current collector may be used in various formsincluding films, sheets, foils, nets, porous structures, foams andnon-woven fabrics.

The conductive material is commonly added in an amount of 1 to 20% byweight, based on the total weight of the mixture containing the cathodeactive material. Any conductive material may be used without particularlimitation so long as it has suitable conductivity without causingchemical changes in the fabricated battery. Examples of conductivematerials include graphite; carbon blacks such as carbon black,acetylene black, Ketjen black, channel black, furnace black, lamp blackand thermal black; conductive fibers such as carbon fibers and metallicfibers; metallic powders such as carbon fluoride powder, aluminum powderand nickel powder; conductive whiskers such as zinc oxide and potassiumtitanate; conductive metal oxides such as titanium oxide; andpolyphenylene derivatives.

The binder is a component which enhances binding of an electrode activematerial to the conductive material and the current collector. Thebinder is commonly added in an amount of 1 to 20% by weight, based onthe total weight of the mixture comprising the cathode active material.Examples of the binder include polyvinylidene fluoride, polyvinylalcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose,regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene,polyethylene, polypropylene, ethylene propylene diene terpolymers(EPDM), sulfonated EPDM, styrene butadiene rubbers, fluororubbers andvarious copolymers.

The filler is optionally added to inhibit expansion of the cathode. Anyfiller may be used without particular limitation so long as it does notcause adverse chemical changes in the manufactured battery and is afibrous material. Examples of the filler include olefin polymers such aspolyethylene and polypropylene; and fibrous materials such as glassfibers and carbon fibers.

The lithium secondary battery generally comprises a cathode, an anode, aseparator and a lithium salt-containing non-aqueous electrolyte, andother components of the lithium secondary battery according to thepresent invention will be described below.

The anode is produced by applying an anode material to an anode currentcollector, followed by drying and the components described above may beoptionally further added.

Examples of the anode active material include carbon such as hardcarbon, graphite-based carbon; metal composite oxides such asLi_(x)Fe₂O₃ (0≦x≦1), Li_(x)WO₂ (0≦x≦1), Sn_(x)Me_(1−x)Me′_(y)O_(z) (Me:Mn, Fe, Pb, Ge; Me′: Al, B, P, Si, Group I, II and III elements,halogen; 0<x≦1; 1≦y≦3; 1≦z≦8); lithium metals; lithium alloys;silicon-based alloys; tin-based alloys; metal oxides such as SnO, SnO₂,PbO, PbO₂, Pb₂O₃, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄,and Bi₂O₅; conductive polymers such as polyacetylene; Li—Co—Ni-basedmaterials and the like.

The anode current collector is generally fabricated to have a thicknessof 3 to 500 μm. Any anode current collector may be used withoutparticular limitation so long as it has suitable conductivity withoutcausing adverse chemical changes in the fabricated battery. Examples ofthe anode current collector include copper, stainless steel, aluminum,nickel, titanium, sintered carbon, and copper or stainless steelsurface-treated with carbon, nickel, titanium or silver, andaluminum-cadmium alloys. Similar to the cathode current collector, theanode current collector includes fine irregularities on the surfacethereof so as to enhance adhesion of anode active materials. Inaddition, the current collectors may be used in various forms includingfilms, sheets, foils, nets, porous structures, foams and non-wovenfabrics.

The separator is interposed between the cathode and the anode. As theseparator, an insulating thin film having high ion permeability andmechanical strength is used. The separator typically has a pore diameterof 0.01 to 10 μm and a thickness of 5 to 300 μm. As the separator,sheets or non-woven fabrics made of an olefin polymer such aspolypropylene and/or glass fibers or polyethylene, which have chemicalresistance and hydrophobicity, are used. When a solid electrolyte suchas a polymer is employed as the electrolyte, the solid electrolyte mayserve as both the separator and the electrolyte.

The lithium salt-containing, non-aqueous electrolyte is composed of anon-aqueous electrolyte and a lithium salt and examples of preferredelectrolytes include non-aqueous organic solvents, organic solidelectrolytes, inorganic solid electrolytes and the like.

Examples of the non-aqueous solvent include non-protic organic solventssuch as N-methyl-2-pyrollidinone, propylene carbonate, ethylenecarbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate,gamma-butyrolactone, 1,2-dimethoxy ethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide,dimethylformamide, dioxolane, acetonitrile, nitromethane, methylformate, methyl acetate, phosphoric acid triester, trimethoxy methane,dioxolane derivatives, sulfolane, methyl sulfolane,1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives,tetrahydrofuran derivatives, ether, methyl propionate and ethylpropionate.

Examples of the organic solid electrolyte include polyethylenederivatives, polyethylene oxide derivatives, polypropylene oxidederivatives, phosphoric acid ester polymers, poly agitation lysine,polyester sulfide, polyvinyl alcohols, polyvinylidene fluoride, andpolymers containing ionic dissociation groups.

Examples of the inorganic solid electrolyte include nitrides, halidesand sulfates of lithium such as Li₃N, LiI, Li₅NI₂, Li₃N—LiI—LiOH,LiSiO₄, LiSiO₄—LiI—LiOH, Li₂SiS₃, Li₄SiO₄, Li₄SiO₄—LiI—LiOH andLi₃PO₄—Li₂S—SiS₂.

The lithium salt is a material that is readily soluble in theabove-mentioned non-aqueous electrolyte and examples thereof includeLiCl, LiBr, LiI, LiClO₄, LiBF₄, LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂,LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li, CF₃SO₃Li, (CF₃SO₂)₂NLi, chloroboranelithium, lower aliphatic carboxylic acid lithium, lithium tetraphenylborate and imides.

Additionally, in order to improve charge/discharge characteristics andflame retardancy, for example, pyridine, triethylphosphite,triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphorictriamide, nitrobenzene derivatives, sulfur, quinone imine dyes,N-substituted oxazolidinone, N,N-substituted imidazolidine, ethyleneglycol dialkyl ether, ammonium salts, pyrrole, 2-methoxy ethanol,aluminum trichloride or the like may be added to the non-aqueouselectrolyte. If necessary, in order to impart incombustibility, thenon-aqueous electrolyte may further include halogen-containing solventssuch as carbon tetrachloride and ethylene trifluoride. Further, in orderto improve high-temperature storage characteristics, the non-aqueouselectrolyte may additionally contain carbon dioxide gas, and may furthercontain fluoro-ethylene carbonate (FEC), propene sultone (PRS) orfluoro-propylene carbonate (FPC).

Effects of Invention

As apparent from the fore-going, the lithium composite transition metaloxide prepared using the transition metal precursor substituted byspecific anions according to the present invention comprises thetransition metal precursor homogeneously present on the surface andinside thereof, thus providing a lithium secondary battery exhibitinghigh charge and discharge efficiency. The process for preparing lithiumcomposite transition metal oxide requires no additional process due toaddition of a compound containing a specific anion and is thus simple,easy and economically efficient.

DETAILED DESCRIPTION OF THE INVENTION

Now, the present invention will be described in more detail withreference to the following examples. These examples are provided only toillustrate the present invention and should not be construed as limitingthe scope and spirit of the present invention.

Example 1

2 L of distilled water was added to a 3 L tank for a wet-type reactorand nitrogen gas was continuously injected into the tank at a rate of 1L/min to remove dissolved oxygen. At this time, a temperature ofdistilled water in the tank was maintained at 45 to 50° C. using atemperature maintenance apparatus. In addition, distilled water presentinside the tank was stirred at a rate of 1,000 to 1,200 rpm using animpeller connected to a motor mounted outside the tank.

Nickel sulfate, cobalt sulfate, and manganese sulfate were mixed at aratio (molar ratio) of 0.40:0.20:0.40 to prepare a transition metalaqueous solution having a concentration of 1.5M. Separately, a 3M sodiumhydroxide aqueous solution containing 0.1 mol % of Na₃PO₄ was prepared.The transition metal aqueous solution was continuously pumped with ametering pump at 0.18 L/hr to the tank for wet-type reactors tank. Thesodium hydroxide aqueous solution was variably pumped such that pH ofdistilled water present in the wet-type reactor tank was maintained at11.0 to 11.5 using a control device connected in order to control pH ofdistilled water in the tank. At this time, an ammonia solution having aconcentration of 30% was also continuously pumped to the reactor as anadditive at a rate of 0.035 L to 0.04 L/hr. An average retention time ofthe solutions in the wet-type reactor tank was adjusted to about 5 to 6hours by controlling flows of the sodium hydroxide aqueous solution andthe ammonia solution. After the reaction in the tank reached a steadystate, the resulting product was allowed to stand for a retention timeto synthesize a density-high composite transition metal precursor.

After the reaction reaches the steady state, a nickel-cobalt-manganesecomposite transition metal precursor prepared by continuously reactingtransition metal ions of the transition metal aqueous solution, hydroxylions of sodium hydroxide and ammonia ions of the ammonia solution for 20hours was continuously obtained through an overflow pipe mounted on thetop of a side of the tank.

The composite transition metal precursor thus obtained was washedseveral times with distilled water and dried in a 120° C.constant-temperature drier for 24 hours to obtain anickel-cobalt-manganese composite transition metal precursor.

Example 2

A transition metal precursor was prepared in the same manner as inExample 1, except that a 3M aqueous sodium hydroxide solution containing0.2 mol % of Na₃PO₄ was used.

Example 3

A transition metal precursor was prepared in the same manner as inExample 1, except that a 3M aqueous sodium hydroxide solution containing0.5 mol % of Na₃PO₄ was used.

Example 4

A transition metal precursor was prepared in the same manner as inExample 1, except that 0.1 mol % of (NH₄)₂HPO₄ was used, instead ofNa₃PO₄.

Comparative Example 1

A transition metal precursor was prepared in the same manner as inExample 1, except that a 3M aqueous sodium hydroxide solution containingno Na₃PO₄ was used.

Experimental Example 1 Content Analysis of PO₄ Ion

0.01 g of each transition metal precursor prepared in Examples 1 to 4and Comparative Example 1 was accurately weighted and added to a 50 mlcorning tube, and a small amount of acid was added dropwise thereto,followed by shaking. The mixed sample was dissolved into a clear stateand a concentration of PO₄ ions in the sample was measured by ionchromatography (model DX500 manufactured by Diones Corp.). Results areshown in the following Table 1.

TABLE 1 Sample PO₄ ion content (wt %) Ex. 1 0.19 Ex. 2 0.40 Ex. 3 1.05Ex. 4 0.20 Comp. Ex. 1 0

As can be seen from ion chromatography analysis results shown in Table1, the content of PO₄ ions in the precursor linearly increased as anamount of the precursor increased.

Experimental Example 2 Measurement of Tap Density

The transition metal precursors prepared in Examples 1 to 4 andComparative Example 1 were tapped 1,000 or more times with a powdermulti-tester (manufactured by Seishin Trading Co., Ltd.) and tapdensities thereof were measured.

TABLE 2 Sample PO₄ ion content (wt %) Ex. 1 1.92 Ex. 2 2.04 Ex. 3 2.20Ex. 4 1.95 Comp. Ex. 1 1.71

As can be seen from ion chromatography analysis results of Table 2, theprecursors containing PO₄ of Examples had extremely high tap densities,as compared to the precursor of Comparative Example.

Example 5 to 8

Each of the nickel-cobalt-manganese composite transition metalprecursors prepared in Examples 1 to 4 and Li₂CO₃ were mixed at a ratio(weight ratio) of 1:1, heated at a temperature increase rate of 5°C./min and then calcined at 950° C. for 10 hours to prepare a cathodeactive material powder of Li[Ni_(0.4)Co_(0.2)Mn_(0.4)]O₂.

The cathode active material powder thus prepared, Denka as a conductivematerial and KF1100 as a binder were mixed at a weight ratio of95:2.5:2.5 to prepare a slurry and the slurry was uniformly coated to analuminum foil having a thickness of 20 μm. The aluminum foil was driedat 130° C. to produce a cathode for lithium secondary batteries.

A 2016 coin battery was produced using the cathode for lithium secondarybatteries, the lithium metal foil as a counter electrode (anode), apolyethylene membrane as a separator (Celgard, thickness: 20 μm) and aliquid electrolyte of 1M LiPF₆ in a mixed solvent containing ethylenecarbonate, dimethylene carbonate and diethyl carbonate at a ratio of1:2:1.

Comparative Example 2

The nickel-cobalt-manganese composite transition metal precursorprepared in Comparative Example 1 was mixed with Li₂CO₃ at a ratio(weight ratio) of 1:1, heated at a temperature increase rate of 5°C./min and calcined at 950° C. for 10 hours to prepareLi[Ni_(0.4)Co_(0.2)Mn_(0.4)]O₂. The Li[Ni_(0.4)Co_(0.2)Mn_(0.4)]O₂ thusprepared was mixed with 1% by weight of Li₃PO₄ to prepare a cathodeactive material powder.

The cathode active material powder was mixed with Denka as a conductivematerial and KF1100 as a binder at a weight ratio of 95:2.5:2.5 toprepare a slurry and the slurry was uniformly coated onto aluminum foilhaving a thickness of 20 μm. The aluminum foil was dried at 130° C. toproduce a cathode for lithium secondary batteries.

A 2016 coin battery was produced using the cathode for lithium secondarybatteries, the lithium metal foil as a counter electrode (anode), apolyethylene membrane as a separator (Celgard, thickness: 20 μm) and aliquid electrolyte of 1M LiPF₆ in a mixed solvent containing ethylenecarbonate, dimethylene carbonate and diethyl carbonate at a ratio of1:2:1.

Comparative Example 3

The nickel-cobalt-manganese composite transition metal precursorprepared in Comparative Example 1 was mixed with Li₂CO₃ in a ratio(weight ratio) of 1:1, heated at a temperature increase rate of 5°C./min and calcined at 950° C. for 10 hours to prepareLi[Ni_(0.4)Co_(0.2)Mn_(0.4)]O₂. The entire surface ofLi[Ni_(0.4)Co_(0.2)Mn_(0.4)]O₂ thus prepared was coated with 1% byweight of Li₃PO₄ using mechanical fusion to prepare a cathode activematerial powder and a 2016 coin battery was then produced in the samemanner as in Comparative Example 2.

Comparative Example 4

The nickel-cobalt-manganese composite transition metal precursorprepared in Comparative Example 1 was mixed with Li₂CO₃ at a ratio(weight ratio) of 1:1, heated at a temperature increase rate of 5°C./min and calcined at 950° C. for 10 hours to prepareLi[Ni_(0.4)Co_(0.2)Mn_(0.4)]O₂. Then, a 2016 coin battery was producedin the same manner as in Comparative Example 2.

Experimental Example 3

Regarding the coin batteries prepared in Examples 5 to 8 and ComparativeExamples 2 to 4, electrical properties of cathode active materials at3.0 to 4.25V were evaluated using an electrochemical analyzer (ToyoSystem, Toscat 3100U). The results are shown in the following Table 3.

TABLE 3 Initial charge/discharge Initial charge/discharge Samplecapacity (mAh/g) efficiency (%) Ex. 5 159.1 90.1 (Ex. 1) Ex. 6 161.291.2 (Ex. 2) Ex. 7 160.4 90.6 (Ex. 3) Ex. 8 159.3 90.3 (Ex. 4) Comp.156.8 88.9 Ex. 2 Comp. 157.4 89.1 Ex. 3 Comp. 157.7 89.2 Ex. 4

As can be seen from Table 3, batteries according to Examples producedusing the precursors treated with PO₄ exhibited improvedcharge/discharge efficiency and thus increased discharge capacity. Thebatteries of Comparative Examples exhibited low charge/dischargecapacity and efficiency, as compared to batteries of Examples.

Experimental Example 4

The coin batteries produced in Examples 5 to 8 and Comparative Examples2 to 4 were charged at 0.2 C and discharged at 0.2 C and 2 C, and ratecharacteristics thereof were evaluated.

TABLE 4 Rate characteristics Sample 2 C/0.2 C (%) Ex. 5 Ex. 1) 90.4 Ex.6 (Ex. 2) 91.5 Ex. 7 (Ex. 3) 90.3 Ex. 8 (Ex. 4) 90.1 Comp. Ex. 2 88.7Comp. Ex. 3 89.1 Comp. Ex. 4 88.7

As can be seen from Table 4, batteries according to Examples producedusing the precursors treated with PO₄ exhibited improved ratecharacteristics and, in particular, the battery according to Example 6produced using the precursor treated with 0.2 mol % of PO₄ exhibitedoptimal performance. The batteries of Comparative Examples usingprecursors not treated with PO₄ exhibited bad 2 C rate characteristics,as compared to batteries of Examples.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A lithium composite transition metal oxide prepared using atransition metal precursor used for preparation of lithium compositetransition metal oxide, the transition metal precursor comprising acomposite transition metal compound represented by the following Formula1:M(OH_(1−x))_(2−y)A_(y/n)  (1) wherein M comprises two or more selectedfrom the group consisting of Ni, Co, Mn, Al, Cu, Fe, Mg, B, Cr andsecond period transition metals; A comprises one or more anions exceptOH_(1−x); 0<x<0.5; 0.01≦y≦0.5; and n is an oxidation number of A.
 2. Thelithium composite transition metal oxide according to claim 2, whereinthe anion A is present in an amount of 0.05 to 3% by weight, based onthe total amount of the lithium composite transition metal oxide.
 3. Thelithium composite transition metal oxide according to claim 1, wherein Mcomprises two or more transition metals selected from the groupconsisting of Ni, Co and Mn.
 4. The lithium composite transition metaloxide according to claim 1, wherein A comprises one or more selectedfrom the group consisting of PO₄, CO₃, BO₃, and F.
 5. The lithiumcomposite transition metal oxide according to claim 1, wherein A is PO₄.6. The lithium composite transition metal oxide according to claim 1,wherein the composite transition metal compound is a compositetransition metal compound represented by the following Formula 2:Ni_(b)Mn_(c)Co_(1−(b+c+d))M′_(d)(OH_(1−x))_(2−y)A_(y/n)  (2) wherein0.3≦b≦0.9; 0.1≦c≦0.6; 0≦d≦0.1; b+c+d≦1; M′ comprises one, or two or moreselected from the group consisting of Al, Mg, Cr, Ti, Cu, Fe and Zr; andA, x, and y and n are as defined in claim
 1. 7. The lithium compositetransition metal oxide according to claim 1, wherein the compositetransition metal compound has a tap density of 1.5 to 2.5 g/cc.
 8. Thelithium composite transition metal oxide according to claim 1, whereinthe composite transition metal compound is present in an amount of 30%by weight or more, based on the total amount of the transition metalprecursor.